The present invention relates generally to vacuum controlling devices and particularly to a device for selectively modifying the vacuum level provided by a variable vacuum source.
Various vacuum responsive devices are used in the fuel or emission systems of internal combustion engines. A common source of vacuum for these devices is the intake manifold of the engine. However, the vacuum created in the engine intake manifold varies significantly with the operation of the engine. Thus, for example, the vacuum in the engine intake manifold becomes minimal or non-existent whenever the engine is given full throttle.
Since the vacuum level required by a vacuum responsive device under certain engine operating conditions may be different than the vacuum level provided by the engine intake manifold, it is desirable to provide an interface between the intake manifold and the vacuum responsive device which is capable of working with the variable intake manifold vacuum to more accurately meet the vacuum level needs of the vacuum responsive device. Preferably, such an interface would take the form of a device which does not require any external energy input and which is inexpensive to manufacture. Additionally, it would be advantageous for this device to be of such a design which permits easy modification in order to be useful in a variety of applications.
Such a device would find particular application in fuel systems which employ an exhaust gas recirculation valve (EGR). As well known in the art, an EGR valve is used to recirculate a portion of the exhaust gases back into the intake manifold of the engine as a way of reducing undesirable exhaust emissions from the engine. Since EGR valves typically operate in response to an applied vacuum, the vacuum in the intake manifold provides a convenient source of vacuum for the EGR valve. However, there are times in which the vacuum generated in the intake manifold does not match the vacuum required by the EGR valve for optimum engine operation. For example, upon the starting of the engine, the vacuum in the intake manifold may quickly become effective to open the EGR valve, even though it may be more advantageous to prevent any exhaust gas recirculation at this time. Additionally, under certain steady state engine operating conditions, the vacuum level in the intake manifold may become insufficient to maintain a desirable opening of the EGR valve.
Furthermore, it is possible for the vacuum level in the intake manifold to fluctuate around the point at which the EGR valve opens. This may result in an undesirable fluttering of the EGR valve. Accordingly, it would be desirable to bypass the critical actuation point of the EGR valve, so that the EGR positively opens and closes only when it is desirable to do so.
While a variety of valve assemblies have been used in the past as interfaces between the engine intake manifold and an EGR valve, such valve assemblies have generally been very complex, and hence costly and not readily susceptible to modifications which would be necessary for use in different applications. These are particularly important considerations in the automobile industry where cost effectiveness and design simplicity are very desirable advantages, especially when a device must be able to respond to several different operating conditions. Thus, for example, the number of components used in a particular design and the number of steps to assemble those components are significant design aspects to suppliers in the automobile industry.
It is therefore a principal objective of the present invention to provide a device which is capable of selectively modifying the vacuum level provided by a variable vacuum source, such as an intake manifold.
It is another objective of the present invention to provide a device which is capable of both maintaining a full vacuum under certain engine operating conditions and reducing the vacuum level under other engine operating conditions.
It is an additional objective of the present invention to provide a device which is capable of being "programmed" to produce a variety of desired vacuum level modifications.
It is a further objective of the present invention to provide a device which is capable of more accurately matching the vacuum level requirements of a vacuum responsive device to a variable vacuum source.
It is yet another objective of the present invention to provide a single self-contained device which can be used to interface an EGR valve to an engine intake manifold, and yet which is also inexpensive to manufacture and assemble.
It is yet an additional objective of the present invention to provide a device which can dampen changes in the intake manifold vacuum level where desirable, and insulate the EGR valve from other changes in the intake manifold vacuum level.
Accordingly, to achieve the foregoing objectives, the present invention provides a device for selectively modifying the vacuum level provided by a variable vacuum source, which generally includes a housing having two inlet ports and an outlet port. The first inlet port is used to provide communication between the housing and the vacuum source, while the second inlet is used to provide communication between the housing and the atmosphere. The outlet port is used to provide communication between the housing and a vacuum responsive device. The device also includes a first valve assembly which is contained in the housing for controlling the communication between the first inlet port and a control chamber in the housing, such that the maximum vacuum level reached by the vacuum source beyond a predeterminable vacuum level is maintained in the control chamber. A passageway is also formed in the housing for providing communication between the control chamber and the outlet port. Additionally, the device includes a second valve assembly in the housing which is responsive to the vacuum level in the control chamber for permitting a predeterminable controlled communication between the second inlet port and the outlet port over a predeterminable vacuum level range.
As will be more fully appreciated from the description below, the first and second valve assemblies cooperate to, in essence, trick the vacuum responsive device into seeing a vacuum level which is at times predeterminably different than the vacuum level currently provided by vacuum source, during both increases and decreases in the vacuum level provided by the vacuum source. Additionally, both the first and second valve assemblies can be readily modified to provide a variety of linear and non-linear functional relationships between the vacuum level provided by the vacuum source and the vacuum level produced at the output port of the device. Importantly, even though the device is capable of providing complex functional relationships between its input and output vacuum levels, it is nevertheless comprised of relatively few components which are easy to assemble. Furthermore, the design of this device also permits the incorporation of the device in an EGR valve to provide a single structure.